It's still a gun that kills the target horribly, just like a real gun, only with insects (It also gives off Thing What Let You Fite Good vibes). Many people will downvote on the core concept alone. You've done a pretty good job actually writing it up, but I don't think the writing's good enough to save it. Heck, I don't know anyone who could write it up well enough while keeping the basic idea intact without radically changing it. I would suggest moving on to a new project.

something that simply makes you want to fire the weapon, whether you have a target or not.

I strongly advise against using compulsions. I've downvoted otherwise decent articles because they added a needless compulsion. The fact that many new authors who cold-post terrible ideas to the mainlist (congrats on not being one of those guys) and add needless compulsions to try and make it scarier means that many people on the site feel the same way about compulsive SCPs.